Interestingly, when the researchers compared the incidence of cardiovascular disease between the two groups, rates were even higher in the trans fat group than the changes in cholesterol and other blood lipids suggested they should be. The NEJM article concluded from several major studies involving 140,000 subjects that an increase of trans fat by just 2% of total energy intake (about 4 grams of trans fat per day, based on the average 2000-calorie-per-day diet) raises the risk of cardiovascular disease by 23%.
The review article also cited studies linking trans fat intake with increased risk of dying from a heart attack or stroke and increased systemic inflammation. It is this chronic inflammation, caused by long-term exposure to various things like smoking, pollution, and bad fats that is thought to be at the root of many chronic diseases, including diabetes.
In another study, which followed almost 85,000 female nurses for 16 years, trans fat intake was shown to increase the risk of diabetes by up to 39% in the nurses who consumed the most trans fat.
Trans fat has also been hypothesized to affect insulin sensitivity and blood glucose levels, which means it may have a very direct effect on day-to-day diabetes management. An article published in Diabetes Care studied 16 obese people with Type 2 diabetes who were placed on three different diets over the course of six weeks. One diet was high in unsaturated fat, the second high in saturated fat, and the third high in trans fat. Although the researchers observed no significant difference in blood glucose levels, the subjects were found to have hyperinsulinemia (overproduction of insulin by the pancreas) after meals on both the high-saturated-fat and high-trans-fat diets. Hyperinsulinemia is linked to insulin resistance, the hallmark of Type 2 diabetes. Other research on glucose and insulin sensitivity has been less conclusive, but it has also not used subjects with diabetes. More research is therefore needed to know what effect the ingestion of trans fat might have on diabetes control.
Why hydrogenate fat?
The hydrogenation process was developed in the early 1900’s and became particularly popular in the years since the 1960’s. In the 1960’s and 1970’s, when it was recognized that saturated fat had unhealthy effects on the body, food companies marketed plant-based margarines and vegetable shortenings as healthier alternatives to butter and lard in home cooking and baking and as good fats in packaged food products. However, there were also practical reasons hydrogenated fats were already being widely used before this time.
For one thing, vegetable oils and hydrogenation are inexpensive. Corn and soybeans are staple crops in the United States, and it is much cheaper to produce oils from these crops than to raise the cattle and swine needed to make butter and lard. In addition, hydrogenated oils do not spoil easily, so packaged goods made with hydrogenated oils have much longer shelf lives than their natural-fat counterparts.
A benefit of partially hydrogenated oils for the consumer is that they spread more easily than animal fats. Have you ever tried to spread cold butter on a piece of toast and watched your toast tear to shreds? Try it with a cold stick of margarine and see how much easier the job becomes. (Full hydrogenation, in contrast, yields a hard, waxlike products.) Not only do partially hydrogenated oils increase spreadability, but they help maintain the emulsion in foods like peanut butter, which means the oil from the peanuts will not separate and rise to the top of the jar. Partially hydrogenated oils also have a very high smoking point, which means they are ideal for frying.
So food manufacturers have had good reasons to use partially hydrogenated oils, but the negative effects they have on health give consumers even better reason to avoid them.